Overload relay



p G, c. ARMSTRONG 2,255,638

OVERLOAD RELAY Filed Jan. 24, 1940 WITNESSES: INVENTOR www U ATTORNEYPatented Sept. 9, 1941 OVER-LOAD RELAY George G. Armstrong,

to Westinghouse E Company, of Pennlyl Wilklnsburg, Pa., assignor lectric8: Mann! East Pittsburgh, Pa., Vania acturing a corporation ApplicationJanuary 24, 1940, Serial No. 315,386

12 Claims.

My invention relates to an overload relay, and more specifically to onethat is responsive to heat generated in response to an overload current.

An object of my invention is to provide an overload relay for use onalternating current circuits, which may be immersed in air or oil andwhich will give outstanding performance on extremely high overloadcurrents.

Another object of my invention is to provide an overload relay which isadjustable in rating.

Other objects and advantages will become more apparent from a study ofthe following specification when considered in conJunction with theaccompanying drawing, in which:

Figure 1 is a side view partly in cross section of an overload relayinvolving the principles of my invention;

Fig. 2 is a modified showing of the movable contact arm; and

Fig. 3 is a sectional view taken along line III-III of Fig. 1.

A coil or winding l carrying the current of the circuit which is to beprotected, and an insulating spool 2 are mounted upon an insulating base3 which is arranged to hold the relay upon a panel by means of suitablemounting bolts (not shown). The insulated casing forms a hermetic sealmaking it possible to operate ,the relay in an oil bath. The coil isarranged to surround a copper tube 4 in which is placed a stationarypole 5 to which is attached on its upper face, a ring 01' an alloy steelmaterial It (for example, Invar") having a curie point preferably above100" C. A nickel-steel alloy having a curie point of about 125 C. is avery suitable example. A movable plunger 6 rests on the magnetic alloyring it and is guided by a brass tube 1.

When the pole piece It is magnetized, the magnetomotive force of thecoil l holds the plunger 6 down tightly against its upper surface. Whenthe current in the coil l, due to an overload, exceeds a particularvalue, eddy currents built up in the copper tube 4 cause the temperatureof the alloy pole piece element I8 to exceed the curie point, and thereis thus a resultant loss in magnetic attraction between the alloy polepiece It and the plunger 6. This results in the plunger being attractedto the upper stationary pole ll driving the operating rod 8 upwards andcausing the separation of the contact members I and Ill. The movablecontact member 8 is normally urged downwardly by a phosphor bronze orsteel spring l3 backed up by a guard I 4.

In contact with the lower pole piece 5 is an the center stud v neticflux which I which when turned about I! may be caused to vary the airgap l2 (see Fig. 3), thereby changing the magcirculates through thecenter oi the coil, and consequently varying the eddy currents set up inthe copper tube 4 and the resultant heating. The circumferential edge ofthe lower ring 20 of the spool may be suitably calibrated and cooperatewith the arrow 2| or other index on disc II. An insulating cap ll of"Moldarta or other suitable insulating material has a tapped insert IIthe eccentric disc ii in position.

The relay as shown rests automatically whenever the coil is deenergized.Hand reset may be provided by arranging a latch (not shown) to catch themovable contact carrying member I! in its open position, holding itthere until manually released. The proportions of the magnetic circuitmay be so arranged as to provide instantaneous trip at high currents asa result of saturation in the parts of the lower pole.

Fig. 2 is a partial cross sectional view taken at right angles to theview in Fig. 1 and showing a bimetallic element 22 which is adjustableby screw 23 and which bimetallic element compensates for changes inambient temperature. The bimetal moves in the direction oi the arrowwhen the ambient increases. The temperature required for tripping may bevaried by adjusting screw 23. The relay may be inverted to keep the coilheat from heating the bimetal.

This adjustable relay may be used either for air operation or for oilimmersion. For oil immersion, slotting (not shown) in the plunger shouldbe provided to by-pass any oil which may leak into the interior of therelay.

eccentric steel disc I The temperature at which the relay operatesmay bedifierent from C. depending on the materials used, the construction ofthe coil, the application (1. e., whether or not it is to be sensitiveto the ambient, etc.).

Although the reversibly magnetic element has been described as being ofa nickel-iron alloy or 01' Invar, it will be apparent that any othermagnetic material which loses or substantially loses its magneticproperty as a result of heat, may be substituted therefor. For example,a nickel copper alloy, often referred to as Monel metal may besubstituted. Likewise, an alloy of iron and nickel, with minorpercentages of silicon or chromium, and which become non-magnetic whenheated to a temperature dependent upon the percentages, may likewise besubstituted.

particularly I am, of course, aware that others,

for adiustably clamping tion, an electromagnetic device 'move under theinfluence of property of substantially aiter having had the benefit ofthe teachings of my invention, may devise other devices embodyingmyinvention, and I, therefore, do not wish to be limited to the specificshowings made in the drawing and the descriptive disclosure hereinbeforemade, but wish to be limited only by the scope of the appended claimsand such prior art that may be pertinent.

I claim as my invention: i

1. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of magnetic pole pieces coaxiallydisposed with respect to said coil, a slidable, plunger type armaturemovable within and along the axis of said coil and which is selectivelyattracted to either of said pole pieces, a reversibly magnetic elementdisposed in the vicinity of one of said pole pieces and which loses itsmagnetism to an appreciable extent as the result of excessive currentflow through said coil thereby allowing the armature to move under theinfluence of the other magnetic pole piece, and an electrical switchwhich is operable by said armature.

2. An overload relay comprising, in combinahaving a coil and a pair ofmagnetic pole pieces coaxially disposed with respect to said coil, aslidable, plunger type' armature movable within and along the axis ofsaid coil and which is selectivelyattracted to either of said polepieces, heating means responsive to current flow through said coil, areversibly magnetic element disposed in the vicinity of one of said polepieces and which loses its magnetism to an appreciable extent as theresult of a predetermined value of heat developed by said heating meansthereby allowing the armature to the other magnetic pole piece, and anelectrical switch which is operable by said armature.

3. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of magnetic pole pieces coaxiallydisposed with respect to said coil, a slidable, plunger type armaturemovable within and along the axis of said coil and which is selectivelyattracted to either of said pole pieces, a metallic member having theproperty of developing a relatively high temperature as the result ofeddy currents induced therein by current flow through said coil, areversibly magnetic element disposed in the vicinity of one of said polepieces and which loses its magnetism to an appreciable extent as theresult of a predetermined value of heat developed by said metallicmember and transferred to said reversibly magnetic element, therebyallowing the armature to move under the influence of the other magneticpole piece, and an electrical switch which is operable by said armature.

4. An overload relay comprising, in combination, anelectromagneticdevice having a coil and a pair of pole pieces coaxiallydisposed with respect to said coil, a reciprocable, plunger typearmature movable within and along the axis of said coil and which isselectively attracted to either of said poles, lar element disposed inthe vicinity of one of said poles, a thin tubular element which iscoaxially disposed with respect to said magnetic tubular element and tosaid coil axis and which is heated as the result of eddy currentsinduced therein by current flow through said coil, said reversiblymagnetic, tubular element having the losing its magnetic property uponbeing heated a predetermined 'amount thereby allowing said armature tobea reversibly magnetic tubu-.

aasaess come attracted by the other of said poles, and

an electrical switch which is operated by said tion, an electromagneticdevice reciprocable armature.

5. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of pole pieces coaxially disposed withrespect to said coil, a reciprocable, plunger type armature movablewithin and along the axis of said coil and which is selectivelyattractedto either of said poles, a reversibly magnetic tubular element disposedin the vicinity of one of said poles, a thin tubular copper elementwhich is .coaxially disposed with respect to said magnetic tubularelement and to said cell axis and which is heated as the result of eddycurrents induced therein by current flow through said coil, saidreversibly magnetic, tubular element having the property ofsubstantially losing its magnetic property upon being heated above 100C. thereby allowing said armature to become attracted by the other ofsaid poles, and an electrical switch which is operated by saidreciprocable armature.

6. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of pole pieces coaxially disposed withrespect to said coil, a reciprocable, plunger type armature movablewithin and along the axis of said coil and which is selectivelyattracted to either of said poles, a reversibly magnetic tubular elementdisposed in the vicinity of one of said poles, a thin tubular elementwhich is coaxially disposed with respect to said magnetic tubularelement and to said coil axis and which is heated as the result of eddycurrents induced therein by current flow through said coil, saidreversibly magnetic, tubular element having the property ofsubstantially losing its magnetic property upon being heated toapproximately 125 (3., thereby allowing said armature to becomeattracted by the other of said poles, and an electrical switch which isoperated by said reciprocable armature.

7. An overload relay comprising, in combinahaving' a'coil and a pair ofmagnetic pole pieces coaxially disposed with respect to said coil, aslidable, plunger type armature movable within and along the axis ofsaid coil and which is selectively attracted to either of said polepieces, a reversibly magnetic element in the vicinity of one of saidpole pieces,

' a thin metallic cylindrical member coaxially disposed with respect tosaid coil and adjacent to said magnetic element and which is heated byeddy currents induced as the result of current flow through said coil,said reversibly magnetic element having a curie point of about C. orabove thereby allowing the armature to move under the influence of theother pole piece upon the attainment of such temperatures by saidreversibly magnetic element, and an electrical switch which is operableby said armature.

8. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of magnetic pole pieces coaxiallydisposed with respect to said coil, a slidable, plunger type armaturemovable within and along the axis of said coil and which is selectivelyattracted to either of said pole pieces, a reversibly magnetic elementof Invar in the vicinity of one of said pole pieces, a thin metallicmember adjacent to said magnetic element and which is heated by eddycurrents induced as the result of current flow through said coil, saidreversibly magnetic element having a curie point of about aasaees 125'(3., thereby allowing the armature to move under the influence of theother pole piece upon the attainment of such temperatures by saidreversibly magnetic element, and an electrical switch which is operableby said armature.

9. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of magnetic pole pieces coaxiallydisposed with respect to said coil, 3, slidable, plunger type armaturemovable within and along the axis of said coil and which is selectivelyattracted to either of said pole pieces, a reversibly magnetic elementdisposed in the vicinity of one of said pole pieces and which loses itsmagnetism to an appreciable extent as the result of excessive currentflow through said coil, thereby allowing the armature to move under theinfluence of the other magnetic pole piece, and an electrical switchwhich is operable by said armature, said electromagnetic device having acore which has an air gap independent of said armature, means forselectively adjusting the width of said air gap.

10. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of magnetic pole pieces coaxiallydisposed'with respect to said coil, a slidable, plunger type armaturemovable within and along the axis of said coil and which is selectivelyattracted to either of said pole pieces, a reversibly magnetic elementdisposed in the vicinity of one of said pole pieces and appreciableextent as the result of excessive current flow through said coil therebyallowing the armature to move under the influence of the other magneticpole piece, and an electrical switch which is operable by said armature,said electromagnetic device having a core which has an air gapindependent of said armature, an eccentrically mounted magnetic memberwhich is adjustable to provide various widths 01' said air which losesits magnetism to an 11. An overload relay comprising, in combination, anelectromagnetic device having a coil and a pair of magnetic pole piecescoaxially disposed with respect to said coil, a slidable, plunger typearmature movable within and along the axis of said coil and which isselectively attracted to either of said pole pieces, a reversiblymagnetic element disposed in the vicinity of one of said pole pieces andwhich loses its magnetism to an appreciable extent as the result ofexcessive current flow through said coil thereby allowing the armatureto move under the influence of the other magnetic pole piece, and anelectrical switch which is operable by said armature, said magnetic polepieces and reversibly magnetic elements being hermetically sealed by acasing thereby adapting the device for immersion in a liquid insulatingmedium.

12. An overload relay comprising, in combination, an electromagneticdevice having a coil and a pair of magnetic pole pieces coaxiallydisposed with respect to said coil, a slidable, plunger type armaturemovable within and along the axis of said coil and which is selectivelyattracted to either of said pole pieces, a reversibly magnetic elementin the vicinity of one of said pole pieces, a thin metallic memberadjacent to said magnetic element and which is heated by eddy currentsinduced as the result of current flow through said coil, said reversiblymagnetic element having a curie point of about C. or above therebyallowing the armature to move under the influence of the other polepiece upon the attainment of such temperatures by said reversiblymagnetic element, and an electrical switch which is operable by saidarmature, said poles, reversibly magnetic elements and thin metallicelements all being hermetically sealed by a. casing, thereby adaptingthe device for immersion in a liquid insulating medium.

GEORGE C. ARMSTRONG.

